This invention is related to an incandescent lamp, and more particularly, to an improved high efficiency incandescent lamp comprising an outer bulb filled with an inert gas or evacuated and an inner envelope containing a halogen atmosphere along with a relatively high pressure fill gas. The inner envelope further houses a separate light-transmissive cylinder having on one of its surfaces a selective infrared reflective film at least partly surrounding a tungsten filament disposed within the cylinder in the inner envelope.
The continuing pursuit of improving the efficiency of lamps is of increasing importance due to the increasing cost of energy. One of the family of lamps in which the efficiency is desired to be improved is the incandescent lamp. Incandescent lamps, although having efficiency ratings lower than those of fluorescent and high intensity discharge lamps, have many attractive features, such as, low cost, compact size, instant light, dimmability, convenience, pleasing spectral distribution, and millions of existing sockets in the homes of users who have become accustomed to the pleasing incandescent type lighting.
Incandescent lamps come in various sizes, the most well-known being that of the A-line which is typically termed a general service incandescent lamp and is available in a wide range of wattage ratings. Such general service incandescent lamps typically employ a tungsten filament. Another incandescent lamp employing a tungsten filament is a Parabolic Aluminized Reflector (PAR) having a built-in reflector for accurate focusing of emitted light to a desired medium.
In typical operation of the general service and PAR incandescent lamps over an extended period of time, some tungsten from the filament evaporates and becomes deposited on the envelope wall, which, in turn, typically causes a darkening of the envelope, which, in turn, decreases the lumen output of the lamps, which, in turn, reduces the lumens per watt or efficacy of the lamps. It is known that the darkening of the envelope caused by the tungsten type filament may be substantially reduced by providing a halogen doped gas atmosphere surrounding the tungsten filament which provides a regenerative (transport) cycle that keeps the envelope wall clean resulting in improved efficacy.
The use of a halogen gas adapted to the relatively inexpensive general service incandescent lamp is described in the previously mentioned U.S. application Ser. No. 519,165, and assigned to the same assignee as the present invention. The halogen atmosphere of the aforementioned U.S. application Ser. No. 519,165 is considered desirable for the present invention along with additional improvements afforded by this invention and related to the general service and PAR incandescent lamps.
The performance of a tungsten filament of the incandescent lamp can be further improved by housing the filament in a suitable fill-gas, such as xenon, krypton or argon, raised to a pressure significantly above atmospheric. The high pressure fill-gas improves the performance of the lamp by reducing the evaporation rate of the tungsten from the filament, thereby increasing the life of the filament when operated at the same temperature. Alternatively, the reduced evaporated rate of tungsten from the filament permits one to raise the filament operating temperature while maintaining the same life. Operating the filament at higher temperatures increases lumens and efficacy.
The arc-out resistance of the filament, that is, the resistance of the filament to being burned out by an arcing condition within its housing, may be improved by the addition of nitrogen. The aforementioned U.S. patent application Ser. No. 519,165 discloses an incandescent lamp utilizing the efficacy gain realized by the high pressure fill-gas of the xenon, krypton or argon, and to improve the arc-out resistance of the filament by the addition of the nitrogen gas. It is considered desirable to operate the tungsten filament within the relatively high pressure fill-gas having nitrogen additive along with further improvements of the present invention.
Another means for extending the life of an incandescent lamp is to reduce the operating voltage of the filament, but it is desired that this reduction of operating voltage be accomplished while maintaining the wattage and efficacy of the lamp. The U.S. patent application Ser. No. 519,165 discloses a specially suited filament that provides extended life and maintains the wattage of the lamp. Alternatively, the efficacy of a low voltage incandescent filament can be increased while maintaining life. Further still, a low voltage filament, such as described in U.S. patent application Ser. No. 519,165, is advantageous in that the low voltage filament is mechanically sturdy with a stable configuration. It is considered desirable to provide a specially suited filament along with further improvement of this invention for a general service incandescent lamp.
Incandescent lamps may also be improved by utilizing an infrared type film. Incandescent lamps employing infrared films are well known. One such incandescent lamp is disclosed in United Kingdom (UK) Patent Specification No. 834,087, published May 4, 1960. The UK Patent Specification No. 834,087 discloses an electric incandescent-filament lamp wherein the filament is at least partially surrounded by a multilayer interference filter which is highly transparent to visible light, but is also highly reflective to infrared radiation. U.K. Specification No. 834,087 discloses one embodiment of filter formed on the surface of a light-transmitting support mounted within the lamp envelope. Although the UK Patent Specification No. 834,087 discloses an infrared film formed on a mounted member within the incandescent lamp, it is considered desired, and a feature of the present invention to provide the incandescent lamp art with an improved incandescent lamp having an infrared film with improved characteristics and disposed on a support member within the incandescent lamp which is arranged in such a manner so as to improve the efficacy of the incandescent lamp.
Accordingly, an object of the present invention is to provide the incandescent art with improved general service and PAR incandescent lamps having (1) a halogen gas atmosphere for efficacy improvements and (2) an inner member with an infrared film so as to further enhance the efficacy of the incandescent lamp.
Other objects of the present invention are to provide the halogen gas atmosphere and the inner member having the infared film in such a manner so as to maintain the relatively inexpensive cost of both the general service and PAR incandescent lamps.
These and other objects of the present invention will become apparent upon consideration of the following description taken in conjunction with the accompanying drawings.